In the present work, N2, N2 + H2, Ar and Ar + H2, were used as the sintering atmosphere of Metal Injection Molded 316L stainless steel respectively. The influences of the sintering atmospheres on C, O, N contents of the sintered specimens, sintered density, grain morphology and mechanical properties were investigated. The results show that C, O, N contents of the sintered specimens can be controlled in permitted low values. The ultimate tensile strength and elongation of the specimen sintered in N2 + H2 atmosphere are 765 MPa and 32% respectively. Using Ar and Ar + H2 as the sintering atmosphere, the density of the sintered specimens is 98% of the theoretical density; the pores are uniformly distributed as small spherical shape and the grain size is about 50 µm. The mechanical properties of the specimen, i. e. ultimate tensile strength 630 MPa, yield strength 280 MPa, elongation 52%, HRB 71, are much better than those of the American Metal Powder Industries Federation (MPIF) 35 Standard after being sintered in Ar + H2.
The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C3H6, C3H6-N2 and C3H6-H2 was investigated respectively. The mechanism on the role of carrier gas in chemical vapor infiltration was also discussed. The results shows that whether or not adding N2 as carrier gas has little influences on the densification behavior of C/C composites with the controlled temperature, the partial pressure of hydrocarbon and the effective residence time of the gas phase remain constant. When the controlled temperature is not less than 1 173 K, using N2 or H2 as carrier gas makes pronounced differences in densifying of C/C composites. The average bulk density of C/C composites from C3H6-H2 is eight to ten percent higher than that from C3H6-N2. However, when the controlled temperature is not higher than 1 123 K, the densification rate of C/C composites from C3H6-H2 is much lower than that from C3H6-N2, which implies that effects of carrier gas on densification of C/C composites are closely related to the type of carrier gas and infiltration temperature. At higher temperature, using H2 as carrier gas is favorable to the densification of C/C composites, while at lower temperature, hydrogen, acting as reactive gas, can inhibit the formation of pyrolytic carbon.
The dynamic recrystallization behavior of 35CrMo steel was studied with compression test in the temperature range of 1 223–1 423 K and the strain rate range of 0.01–10.00 s−1. The initiation and evolution of dynamic recrystallization were investigated with microstructure analysis and then the critical strain ɛc for dynamic recrystallization initiation, the strain for maximum softening rate ɛ* and the steady strain ɛs were obtained to be 2.92×10−3Z0.1381, 1.60 × 10−3Z0.1780 and 3.26 × 10−2 × Z0.0972 respectively by analysis of work-hardening rate-strain θ-ɛ curves, where Z is the Zener-Hollomon parameter. The dynamic recrystallization fraction was determined using recrystallization theory, and the effects of initial grain size, strain rate and deformated temperature on the dynamic recrystallization kinetics were investigated. The results show: , the dynamic recrystallization fraction is slightly delayed due to the somewhat larger initial grain size and markedly delayed with the decrease of temperature. On the other hand, it is significantly accelerated with the increase of the strain rate. Finally, the relationships between the initiation time, ending time of dynamic recrystallization and the deformed temperature were analyzed in detail.
Thermodynamic calculation on the smelting slag of direct recycling of electric arc furnace stainless steelmaking dust was presented. An induction furnace was used to simulate electric arc furnace smelting to recover the metals from the dust. The elements of iron, chromium and nickel in the ingot and the components of metal oxides in the slag were analyzed. The thermodynamic model for FeO-Cr2O3-MgO-SiO2 slag was set up and the active concentrations of substances in the slag at 1 550 °C were determined by thermodynamic calculation according to the experimental data. The results show that the apparent equilibrium constant and quantitative distribution of chromium between slag and steel are unstable and affected by the mass ratios of pellets to start iron and metal reducing agent to the pellets. In order to get satisfactory chromium recovery from the direct recycling of electric arc furnace stainless steelmaking dust, it is important to ensure the mass ratio of pellets to the steel below 0.20 and the mass ratio of metal reducing agent to pellets over 0.18 in practical smelting runs.
The ultra-fine-grinding and resin-in-pulp with pH value of 10 are used to extract gold from pyrite roster cinder. During leaching process, aluminium oxide ball is used as stirring medium, hydrogen peroxide as leaching agent and sodium hexametaphosphate as grinding agent. With AM-2σ resin as absorber and sulfocarbamide as eluent, gold is recovered from cyanide pulp of pyrite roster cinder by resin-in-pulp. The effects of contact time, temperature and acidity etc. on the gold absorption are investigated by static methods and dynamic method respectively. The effects of flow rate of solution on dynamic adsorption and elution of gold are studied. The results show that AM-2σ resin has good adsorbability in cyanide solution, and gold can be easily eluated from the loaded resin with 0.1mol/L hydrochloric acid and 1mol/L sulfocabamide. The adsorption rate and the elution of gold exceed 98%. When leaching time is 2 h, mass ratio of liquid to solid 4:1, consumption of sodium cyanide 3 kg/t, concentration of hydrogen peroxide and sodium hexametaphosphate 0.05% respectively, adsorption time 30 min, temperature 10–30 °C, volume of resin 3 mL, ratio of eluent to resin (10–20):1, velocity of eluent 1.5 mL/min, the leaching rate of gold reaches 85%. Compared with traditional leaching technology, it can reduce leaching time, avoid complex filter process, decrease sodium cyanide consumption and increase leaching rate of gold by 35%.
The influence of four kinds of Schiff bases on a strain of Escherichia coli was studied by microcalorimetry. Differences in their capabilities of suppressing the metabolism of this bacterium were observed. The results show that the extent and duration of the inhibitory effect on the metabolism as judged from the multiplication rate constant, k, varies with different Schiff bases. The multiplication rate constant k, of Escherichia coli (in log phase) in the presence of Mo-salicylioaldehyde-thiadizole, Mo-piperonaldehyde-thiosemicarbazone and Mo-3-methoxy-salicylicaldehyde-thiadizole decreases with the increase of concentrations of compounds c, and the relationships between k and c, maximum heat production rate pm and c, peak time of growth curves tp and c are of linearity. For Mo-6-nitro-pieronalde-thiosemicarbazone, the multiplication rate constant is constant irrespective of variation in concentration. The sequence of antibiotic activity of Schiff base is: Mo-salicylioaldehyde-thiadizole>Mo-3-methoxy-salicylicaldehyde-thiadizole>Mo-piper-onaldehyde-thiosemicarbazone >6-nitro-pieronalde-thiosemicarbazone.
The effect of additive RCOONa on the formation of MnZn ferrite homogeneous coprecipitation precursor was studied in this paper. The action of additive in the MnZn ferrite hydrothermal crystallization process was investigated according to crystal field theory and crystal growth unit theory. And the growth unit formation process was presented and its structure was illustrated. The results show that the precursor of MnZn ferrite is a colloidal mixture composed of Zn(OH)2, Fe(OH)2, Mn(OH)2, MnO(OH), MnO2·xH2O and so on, and dissolves in solution in the form of hydroxyl coordination tetrahedron and octahedron such as Zn(OH)42−, Fe(OH)42−, Fe(OH)64−, Fe(OH)4−, Fe(OH)53−, Mn(OH)42−, Mn(OH)63− etc., and the growth unit is formed by combination of the coordination polyhedra subsequently in the hydrothermal precess. The additive is beneficial to the formation of homogeneous precursor and has dispersive effect on the aggregation of the crystal growth unit by forming associate with hydrogen bond, which is beneficial to the synthesis of the pure product with a tiny size and a narrow size distribution.
Distribution behavior of terbutaline enantiomers was examined in the aqueous and organic solvent of a two-phase system containing L-dibenzoyltartaric acid and lipophilic phase transfer reagent of Na-tetraphenylborate. The influences of pH, organic solvents, concentrations of Na-tetraphenylborate and L-dibenzoyltartaric acid on the partition coefficients and enantioselectivity of terbutaline enantiomers, were investigated. The results show that tetraphenylborate lipophilic anion and terbutaline enantiomers form two lipophilic salt complexes, which facilitates the solubility of the enantiomers in the organic phase. L-dibenzoyltartaric acid forms more stable complexes with enantiomer II than with enantiomer I. Enantioselectivity and partition coefficient increase with the addition of the length of alkyl chain of alcohols. pH and concentrations of lipophilic anion and L-dibenzoyltartaric acid influence them obviously and differently.
Nanometer zinc oxide was prepared by solid phase reaction. And the ultraviolet-visible spectral properties of nanometer zinc oxide colloidal solution dispersed in both water and oil phases were studied. The results show that the absorbance of the colloidal solution to ultraviolet light increases with the decrease of wavelength and reaches about 2.5 at the wavelength of 200 nm. When the mass fraction of nanometer zinc oxide becomes lower, the transmittance of the colloidal solution to visible light gets higher, and it is much higher than that of normal zinc oxide under the same conditions, indicating that nanometer zinc oxide dispersed in both water and oil phases has high transmittance to visible light and good shield to ultraviolet light. Therefore it is suitable for the replacement of organic ultraviolet absorber and titanium dioxide in cosmetics.
A QoS routing protocol based on mobility prediction is proposed. The protocol selects the steadiest path based on mobility prediction and QoS requirements on bandwidth, delay, and so forth. The main properties of the protocol as follows. (1) Each node just broadcasts its own information, so the packet is very small and can get to the destination in a very short time. (2) When another path is built for the same QoS requirements, the original path has higher priority. (3) The update messages are reduced by using mobility prediction. (4) Data packets carry the information of link change using piggyback, which is helpful for forecasting the link status more accurately. (5) When source node gets Resource-Reserve and reconnect packets at the same time, it selects reconnect packet over Resource-Reserve packet. The results of simulation show that the protocol has good network performance with low control overload, and efficiently supports transmitting multimedia with QoS requirements in mobile ad hoc networks.
Formulizations of mutation and crossover operators independent of representation of solutions are proposed. A kind of precisely quantitative Markov chain of populations of standard genetic algorithms is modeled. It is proved that inadequate parameters of mutation and crossover probabilities degenerate standard genetic algorithm to a class of random search algorithms without selection bias toward any solution based on fitness. After introducing elitist reservation, the stochastic matrix of Markov chain of the best-so-far individual with the highest fitness is derived. The average convergence velocity of genetic algorithms is defined as the mathematical expectation of the mean absorbing time steps that the best-so-far individual transfers from any initial solution to the global optimum. Using the stochastic matrix of the best-so-far individual, a theoretic method and the computing process of estimating the average convergence velocity are proposed.
The finite element analysis and the optimum design of aluminum profile extrusion mould were investigated using the ANSYS software and its parameterized modeling method. The optimum dimensions of the mould were obtained. It is found that the stress distribution is very uneven, and the stress convergence is rather severe in the bridge of the aluminum profile extrusion mould. The optimum height of the mould is 70.527 mm, and the optimum radius of dividing holes are 70.182 mm and 80.663 mm. Increasing the height of the mould in the range of 61.282 mm to 70.422 mm can prolong its longevity, but when the height is over 70.422 mm, its longevity reduces.
Static secure techniques, such as firewall, hierarchy filtering, distributed disposing, layer management, autonomy agent, secure communication, were introduced in distributed intrusion detection. The self-protection agents were designed, which have the distributed architecture, cooperate with the agents in intrusion detection in a loose-coupled manner, protect the security of intrusion detection system, and respond to the intrusion actively. A prototype self-protection agent was implemented by using the packet filter in operation system kernel. The results show that all the hosts with the part of network-based intrusion detection system and the whole intrusion detection system are invisible from the outside and network scanning, and cannot apperceive the existence of network-based intrusion detection system. The communication between every part is secure. In the low layer, the packet streams are controlled to avoid the buffer leaks existing in some system service process and back-door programs, so as to prevent users from misusing and vicious attack like Trojan Horse effectively.
Based on principles of electromagnetic fluid dynamics the exerted forces and movement states of melted aluminum in the traditional reduction cells and the drained cells were compared and analyzed in this paper. And based on the theory of slow movement, a formula in respect of the drained angle was derived, i. e. . It can be seen that the drained slope can be decided by respectively multiplying the area current densities and magnetic induction intensities in three coordinate directions in aluminum reduction cells, and the drained slope is approximate to 0.6% derived from typical data based on measurement and calculation, which implies that the key parameter is obtained in designing of drained cells. The results can be used for a designing basis for drained cathodes.
An efficient binomial lattice for pricing Asian options on yields is established under the affine term structure model. In order to reconnect the path of the discrete lattice, the technique of D. Nelson and K. Ramaswamy is used to transform a stochastic interest rate process into a stochastic diffusion with unit volatility. By the binomial lattice and linear interpolation, the prices of Asian options on yields can be obtained. As the number of nodes in the tree structure grows linearly with the number of time steps, the computational speed is improved. The numerical experiments to verify the validity of the lattice are also provided.